Page 675 - Industrial Power Engineering and Applications Handbook

19/640 Industrial Power Engineering and Applications Handbook
100% Puffer technique
Destabilization of the arc plasma is achieved by forced
convection of gas created by the movement of the main
and arcing contacts through a puffer piston. This is an
integral part of the moving main and arcing contacts
(both being concentric). In the light of more advanced
techniques of arc extinction now available, the manufacture
of such breaker is now limited to about 145 kV.

Sequence of arc quenching
Refer to Figure 19.17. On a trip signal the main moving
50% contacts start separating alittle ahead of the moving arcing
contact and compress gas through the puffer piston inside
the tubular chamber. On separation the main fixed and
moving contacts are transferred to the fixed and the moving
33% arcing contacts as shown. As soon as the moving arcing
contact starts separating, an arc is formed between the
25%
fixed and the moving arcing contacts and the already
moderately compressed gas is compressed further. This
compressed gas is impinged with full force through the
blast nozzle (Figure 19.18) at right angles to the arc plasma
from all sides to achieve instant destabilization of the arc.
Through radiation also, the arc plasma dissipates a
Puffer The r m a I Arc Double part of its heat which supplements the quenching. But
blast assisted volume this is too meagre a contribution, as heat dissipation occurs
only through the outer surface of the arc plasma.
Nevertheless, it is the major cause of gas impediment
Figure 19.16(c) Comparison of energy requirement for arc giving rise to the phenomenon of clogging, discussed
extinction in an SF, breaker, using different techniques later, and which helps in ai extinction.
(Courtesy: Alstorn)

Pole in closed position. Mai Pole at the moment of Pole after arc
and arcing contacts closec separation of arching contac quenching

@ - Fixed arcing contact @ - Main fixed contact @ -Arc chute
0- Tubular gas (blast) chamber @ - Main moving contact @ - Moving contact assembly
0 Puffer piston @ - Fixed contact assembly
-
Figure 19.17 Sequence of arc extinction through the puffer technique in an SF6 breaker through the cross-section of a pole
(Courtesy: NGEF Ltd.)